The gastrointestinal microflora plays a number of vital roles in maintaining gastrointestinal tract function and overall physiological health. The growth and metabolism of the many individual bacterial species inhabiting the gastrointestinal tract depend primarily upon the substrates available to them, most of which are derived from the diet. See, e.g., Gibson G. R. et al., 1995 Gastroenterology 106: 975-982; Christl, S. U. et al., 1992 Gut 33: 1234-1238. These findings have led to attempts to modify the composition and metabolic activities of the bacterial community through diet, primarily with probiotics, which are live microbial food supplements.
Probiotic organisms are non-pathogenic, non-toxigenic, retain viability during storage, and typically survive passage through the stomach and small intestine. Since probiotics do not generally permanently colonize the host, they need to be ingested regularly for any health promoting properties to persist.